Most of printed circuit boards available today are powered by two power supplies, whose voltage is respectively 5 volts and 3.3 volts. This is because some high density modules to be installed on the board require a voltage of 5 volts while other high density modules require 3.3 volts.
However, interchangeable modules are available to perform the same functions. Namely, when mounting the modules on the board, a 5-volt module can be replaced with another component requiring a 3.3-volt power supply. In such a case, both modules are pin-compatible, which means that they have the same contacts or footprints, so that the first module can easily be replaced with the second one with no need to modify the board.
Unfortunately, since the power supply is not the same for both modules, the connection of the second module footprints to the power supply is different from the connection of the first module footprints to the other power supply. Two solutions are then possible if using two boards is unwanted. The first solution consists in connecting by means of straps at the time of mounting, the module footprints to the vias that link the suitable power supply of the board. In the second solution, the board is already provided with connecting tracks with two vias, each via being connected to one distinct power supply. In the latter case, it is thus necessary to scrape off one connecting track. In both cases, the tasks are tedious and expensive when there are many footprints (for example 16 footprints).